The translational control of protein synthesis by hemin in rabbit reticulocytes is mediated by the formation of a high molecular weight protein inhibitor of polypeptide chain initiation termed the hemin controlled translational repressor (HCR). Recent work has indicated that HCR acts as a specific protein kinase by phosphorylating the initiation factor (eIF-2) that mediates binding of the initiator tRNA (Met-tRNAf) to 40 s ribosomal subunits. We intend to determine what effect phosphorylation of eIF-2 has on the activity and distribution of this factor and on its ability to cycle. We plan to isolate and characterize the phosphatase in reticulocyte lysate that dephosphorylates eIF-2. We will also determine what role deacylation of subunit bound Met-tRNAf plays in the action of HCR, and, if indicated, we will isolate and characterize the ribosomal Met-tRNAf hydrolase that may mediate this effect of HCR. Finally, the effect of HCR on the steps in polypeptide chain initiation will be determined using ribosomal components isolated from reticulocyte lysate by chromatography on Sepharose 6B.